1. Field of the Invention
The present invention relates to a resin composition which is excellent in heat resistance and impact resistance. Also, the present invention relates to a resin composition which is hard to get decomposed by heat and less suffering from coloring during molding operation.
2. Description of the Prior Art
Heat resistant ABS resins, modified polyphenylene ether resins and polycarbonate resins have been employed in the fields requiring heat resistance.
Heat resistant ABS resins have been produced by a so-called graft blending process in which a graft ABS resin prepared by polymerizing acrylonitrile, and styrene and/or .alpha.-methylstyrene in the presence of a butadiene rubber is blended with a matrix resin such as a ter-polymer of acrylonitrile-styrene-.alpha.-methylstyrene or a quadri-polymer of acrylonitrile-styrene-.alpha.-methylstyrene-N-phenyl maleimide. In these cases, use of .alpha.-methylstyrene involves drawbacks that the rate of polymerization is slow and preparation of a copolymer with a high degree of polymerization is difficult, as well as that the copolymer is easily decomposed by heat at the time of processing since a structure of repeated .alpha.-methylstyrene chains is formed in the copolymer. Further, a maleimide copolymer is disclosed in Laid-Open Japanese Patent Applications Tokkai-Sho 58-162616, 60-79019 and 61-276807. The copolymer using N-phenyl maleimide is often prepared by emulsion polymerization but such copolymer is not preferred since the development of impact resistance is poor due to the effect of an emulsifier remained in the copolymer and coloration of the copolymer is remarkable during molding operation.
On the other hand, modified polyphenylene ether resins, polycarbonate resins and modified polycarbonate resins have drawback that they are generally expensive and poor in moldability.
In the case of preparing a highly heat resistant copolymer using maleimide monomer, although the use of maleimide monomer by more than a certain amount is necessary, if the maleimide content in the copolymer is increased excessively, the resultant copolymer is poor both in the impact resistance and fluidity. Accordingly, monomer composition to be charged to a polymerization reactor has to be adjusted within a certain range. In addition, since the maleimide monomer shows much higher rate of polymerization and tends to cause homopolymerization, the molecular weight distribution or the distribution of chemical composition in the copolymer becomes broader tending to worsen the physical property such as the impact resistance of the copolymer. Further, if unreacted maleimide monomer is present in the copolymer, transparency of the copolymer is reduced and its coloration is remarkable. In view of the above, sufficient consideration has to be taken for polymerization process and subsequent devolatization of the unreacted monomer and organic solvent.
As the results of the research and development of such copolymers it has been found that a resin composition having an excellent heat resistance and impact resistance can be prepared by continuously polymerizing a maleimide monomer with other monomers at a specific ratio in the presence of a predetermined amount of an organic solvent by a specific method, devolatizing unreacted monomers and the organic solvent in a devolatizing device and then blending the resultant maleimide copolymer with a specific rubber-reinforced resin.